Reproductive performance of postpartum dairy cows under a highly intervenient breeding program involving timed insemination and combinations of GnRH,prostaglandin F-2 alpha and human chorionic gonadotropin

Lactating Holstein cows (n=288) were grouped as pairs at parturition and ra ndomly assigned to two treatments (control, C vs intervenient treatment, T) . The reproductive management of the Group C cows (n=130) consisted of the intramuscular administration of 500 mug PGF(2 alpha) analogue (PG) on Days 28 and 63 postpartum and breeding on the basis of estrus signs with the a.m .-p.m. rule after Day 63. Cows that were not bred by 77 d postpartum receiv ed another injection of PG and were bred at estrus or 84 h after PG treatme nt. Pregnancy diagnoses were performed by palpation of the uterus per rectu m 42 to 48 d after Al. Cows in the T group (n=139) received intramuscular i njections of 100 mug GnRH 14 d and PG 28 d after calving. On Day 56 postpar tum, cows were given a second dose of GnRH followed by PG on Day 63 postpar tum and a third GnRH injection 48 h after PG(OvSynch). Cows were inseminate d at a fixed time (22 +/-1 h) after GnRH. Five days after the fixed-time in semination cows were given 1500 IU hCG im. Group C and T cows that returned to service or were diagnosed as non-pregnant continued to receive PG at in tervals of 14 d with breeding at estrus or 84 h after the second PGF(2 alph a) dose. A sustained increase in milk progesterone concentration was observ ed in 59.0% of T cows after GnRH administration on Day 14. A similar rise i n milk progesterone concentrations was observed in 53.8% of C cows. The PG on Day 28 induced luteolysis more in Group T cows (53.2%) than in Group C c ows (36.9%). The PG on Day 63 reduced milk progesterone concentrations to b asal levels in 50.7% of T and 49.2% of Group C animals. The first service p regnancy rates (T, 40.3% vs C, 36.2%) and the overall pregnancy rates tall services, T, 83.5% vs C, 86.9%) were not different between the two groups. The two treatments did not differ in the interval from first service to pre gnancy, calving to pregnancy or in calving interval, number of services per pregnancy or culling rates. (C) 2001 by Elsevier Science Inc.